Toppik Hair Fibers will last until you wash your hair with shampoo. It's possible they may start to fall out depending on your activity, for example, if you go for a swim. You can use hair spray ...

Hair fibers aren't cheap (it's best to use them sparingly so they last and so they blend better). I like to stock up when they're on sale, but Toppik only goes on sale about once a season.